With the development of the ability to bond material to teeth, more particularly to tooth enamel, orthodontics was presented with bondable brackets and attachments. The strength of the bracket bond to a tooth was determined by the combination of the strength of the bond to the tooth, the strength of the bonding material, and the strength of the bond to the orthodontic attachment. The bond to the orthodontic bracket was facilitated by using bonding materials, such as acrylics, which readily formed a strong union with the bracket. Metal brackets and other attachments were developed with a mesh-type bonding surface that produced a semi-mechanical lock with the bonding material. Plastic brackets were easily broken and absorbed stains. Ceramic brackets were then developed.
Ceramic brackets, as described in U.S. Pat. No. 4,948,366, were made from mono-crystalline or poly-crystalline aluminum oxide, which were resistant to staining. The bonding surface of the ceramic bracket was treated with a silane coupling agent in order to enhance the strength of the bond with the bonding material. The ceramic material was similar to a diamond, hard and brittle, resulting in a surface hardness greater than that of tooth enamel. If the ceramic bracket had an occlusal interference it would abrade the enamel of the opposing teeth. The orthodontic company rushed to market with this new product by advertising directly to the public, which created a public demand for the product before adequate clinical trials had been performed. Clinically, the orthodontist found that when attempting to remove the ceramic bracket from a patient's tooth, the tooth enamel would occasionally detach with the ceramic bracket. The strength of the ceramic bracket to enamel bond was greater than the enamel to the underlying tooth. Research revealed that the smooth bonding surface of the ceramic bracket treated with a silane-coupler greatly enhanced the attachment of the bonding material to the ceramic bracket. It was also found that this type of flat surface on the ceramic bracket produced a very thin layer of bonding film, which in turn produced a stronger bond. The thinner the bonding film the stronger the bond.
Ceramic brackets are often removed with the jaws of an orthodontic pin cutter by placing the cutting edges between the bracket base and the tooth and squeezing. The orthodontic ceramic bracket would often fracture upon attempted removal from the tooth, leaving a piece of the ceramic bracket still bonded to the tooth. At this point a dental drill would often have to be used to remove the piece of ceramic bracket from the tooth. The dental drill was not a perfect solution due to the nature of the hardness of the porcelain bracket. The dental drill most commonly used was diamond-coated, which had close to the same hardness as the porcelain bracket, and which was harder than tooth enamel. The ceramic bracket was also the same color as tooth enamel. Thus, tooth enamel could be inadvertently removed.
The mesh-backed metal brackets were more successful than the ceramic bracket. The mesh-backed metal bracket produced a greater thickness of bonding material, allowing enough space between the bracket and the tooth to allow the pin cutter to more easily wedge between the bracket and tooth and remove the bracket when the pin cutter jaws were squeezed together. The metal brackets would not fracture as the porcelain brackets did. The early metal brackets also had the ability to flex, wherein twin brackets could be gripped and squeezed by a pair of pliers, which broke the bond. Modernly, metal brackets are formed by metal injection molding and do not possess this flexing ability yet still will remain in one piece during removal.
Several attempts have been made to solve the debonding problem associated with ceramic brackets. For example, it was proposed in U.S. Pat. No. 4,455,138 that applying heat to the dental bracket would assist in loosening the adhesive bonding of the bracket to the tooth so that the ceramic bracket may be more easily removed with less force. It was found that this system was not always practical as the orthodontist may prematurely pull the bracket in anticipation of the loosening of adhesive, causing great pain to the patient and also shattering the bracket before the heat applied would loosen the adhesive. Further, the pulling force could not be directionally controlled with this system. In addition, the high temperatures associated with this method of removal could cause pulpal or nerve damage to the tooth.
Another debracketing tool and method of removal is disclosed in U.S. Pat. No. 4,907,965, where the heat and debracketing force is simultaneously applied. This system does not always assure that the adhesive is sufficiently loose to allow easy removal, and likewise requires engagement of the ceramic bracket during removal. In addition, the high temperatures associated with this method of removal could cause pulpal or nerve damage to the tooth.
A relatively flexible bonding pad is described in U.S. Pat. No. 5,098,288, wherein a bonding pad is secured to the bracket and bonded to the surface of a tooth. The attached pad is gripped by pliers, causing a buckling of the pad, breaking the bond between the pad and the tooth. The purpose was to prevent fracturing of the bracket during the removal process. However, the flexibility of the bonding pad does not allow for higher bonding strengths between the bonding pad and the enamel surface. In fact, increasing bonding strengths between the bonding pad and the enamel surface decreases flexibility of the bonding pad.
U.S. Pat. No. 5,263,859 describes a flexible bonding pad with holes, allowing the bonding material to come in direct contact with the bracket. The purpose was to increase the strength of the bond to the bracket. However, the flexibility of the bonding pad does not allow for efficient bonding strengths between the bonding pad and the enamel surface. In fact, increasing bonding strengths between the bonding pad and the enamel surface decreases flexibility of the bonding pad.
U.S. Pat. No. 6,786,720 discloses a light-curable methacrylate-based epoxy resin bonding pad molded to a ceramic orthodontic appliance. Debonding is performed by squeezing the pad with ligature cutters, causing the bracket to release from the tooth. However, the flexibility of the bonding pad does not allow for efficient bonding strengths between the bonding pad and the enamel surface. In fact, increasing bonding strengths between the bonding pad and the enamel surface decreases flexibility of the bonding pad.
Another factor involving orthodontic brackets is the unintentional debonding during the patient's treatment which is time-consuming for the orthodontist, and often delays the completion of the patient's treatment. Most commonly, the patient has eaten something too hard. Orthodontics is moving toward digitally-assisted bracket placement. If one failure occurs in treatment, it is virtually impossible to replace the bracket in the same position. With the trend in extended appointment intervals (from traditional 4-week intervals to current 8-10-week intervals), a broken bracket can greatly add additional treatment time and significant cost to the orthodontist due to the process involved to repair the unintentionally broken bond. The dilemma is that orthodontic bond strengths must be strong enough to adhere brackets to teeth yet weak enough that upon removal they do not fracture enamel, causing damage to the teeth. Further, the pulling force could not be directionally controlled with this system.
U.S. Pat. No. 7,819,660 discloses appliances that are not designed to resist or distribute masticatory shear forces of an occlusal gingival direction. The appliances rely on an expensive multitude of bracket bodies with different x-axis, y-axis, and z-axis positions.
Another debracketing tool and method of removal is disclosed in U.S. Pat. No. 4,907,965, wherein heat and debracketing force is simultaneously applied. This system does not always assure that the adhesive is sufficiently loose to allow easy removal, and likewise requires engagement of the ceramic bracket during removal. In addition, the high temperatures associated with this method of removal could cause pulpal or nerve damage to the tooth.
It is also known to provide a relatively flexible bonding pad or base for an orthodontic bracket to facilitate debonding, as disclosed in U.S. Pat. No. 5,098,288. However, it has been found that the bonding between the pad and the bracket often fails during treatment due to the various forces on the bracket during treatment, thereby necessitating re-bonding. Further, the flexibility of the bonding pad does not allow for efficient bonding strengths between the bonding pad and the enamel surface. In fact, increasing bonding strengths between the bonding pad and the enamel surface decreases flexibility of the bonding pad. In such instances, treatment has been interrupted, delaying the ultimate conclusion of treatment, and costly chair time is required to re-bond the bracket to the tooth.